Electric utilities have sub-stations which receive electricity from a generating station for transmission to customers in the service area of the sub-station. Many sub-stations have two transformers each supplying part of the load, one supplying power to one set of customers and the other supplying power to other customers.
It is common practice to provide for the failure of one of the transformers by a throwover control system which automatically transfers all of the load normally carried by the failed transformer to the other transformer. Such throwover control systems work satisfactorily as long as the total demand load on the two transformers does not exceed the capacity of either one transformer. One object of this invention is to provide a means for monitoring the total demand load on both transformers and for automatically blocking the operation of the throwover control when total demand load exceeds the capacity of either transformer.
Other objects will become more apparent as the following description proceeds, especially when considered with the accompanying drawings.